Method of making formic acid.



ther stated therein The mixin nnrrnn s'ra'rns rirrnnr orricn.

HENRY HOWARD, 0F BOSTON, MASSACHUSETTS.

METHOD OF MAKING FQRMIC ACID.

No Drawing.

To all whom it may concern:

Be it known that I, HENRY HOWARD, a citizen of the United States, residing at Boston, in the county of Sufiolk and State of Massachusetts, have invented certain new and useful Improvements in Methods of Making Formic Acid, of which the following is a specfication.

presence of concentrated sulfuric acid the transformation of the dry formates could only be effected with sulfuric acid having a strength of at most 60 Baum. It is furof the dry formate with the sulfuric aci cannot for various reasons be effected so exactly as to obtain a good yield. Thus if high-concentrated'sulfuric acid is'allowed to drop on formate a very considerable rise of temperature locally occurs which cannot be removed by cooling, as in the'mass lumps or the like are formed, so that the mass becomes thick and cannot be stirred, and the sulfuric acid being not rapidly combined.com es in contact with the formic acid set free and decomposes the same. I have discovered that although these statements are col rect as applied to a method wherein highly concentrated sulfuric acid is added to commercial sodium formate, they are not applicable to a method wherein the formate is added to a bath of sulfuric acid. In case sulfuric acid of high concentration be added to sodium formate or dropped thereon, particularly if the formate contains such considerable pro-' portions of water as are usually found in the commercial salt, an intense local heating ocacid may be wholly or partiallyaccounted for as follows: When sulfuric acid is added to sodium formate, particularly such as con- Specification of Letters Patent.

Patented June '7, 19112.

Application filed. June 23, 1908. Serial No. 440,024.

tains an appreciable percentage of moisture, a local rise of temperature occurs at the region of contact and a considerable quantity of formic acid is there produced; this acid being an excellent solvent for sodium formate and being by the consistence of the mass prevented from rapidly diffusing therethrough provides conditions under which the reaction proceeds with great rapidity, the development of heat being so rapid that the temperature cannot be efiectively controlled. \Vhen however the formate is added to a bath of sulfuric acid, even though the latter be of quite high concentration, the bath being suitably agitated, such formic acid as is produced is immediately distributed throughout the mass and does not under these conditions exert so'rapid solvent action upon the formate; inasmuch as the formate is slowly or difficult-1y soluble in strong sulfuric acid the conditions do not lead to the rapid progress of the reaction or to a rapid development of heat. Furthermore, by reason of the excellent heat-conducting properties and high'specific heat of sulfuric acid, as well as owing to the fluidity of the bath, the heat is quickly diffused throughout the mass and only a relatively slight rise of temperature is observed: Under these conditions any of the usual cooling means are effective to maintain a constant temperature below acid. In order to proceed with the minimum loss of formic acid by decomposition, it is therefore important that the temperature should be kept as low as practicable during the initial stages of the reaction; and it is preferred to maintain throughout the mass, during the initial stages of the decomposition, a temperature not exceeding 50 C.

The process may be carried into efi'ect by providing a jacketed mixing vessel ada ted to withstand sulfuric acid, supplying sul uric acid of the desired concentration, and-slowly f any...

adding to the bath the theoretically requisite quantity of sodium formate, the mixture being cooled as required. Thereafter the temperature may be raised by admitting steam to the jacket, and the formic acid is distilled over, reduced pressure being used if preferred. It has been found that by proceeding in this manner sulfuric acid containing up to 88 per cent. of H 80, may be employed and a substantially theoretical yield of formic acid obtained. The described method of procedure is highly eflicient even with acid of higher concentration.

I claim i 1. In a method of making formic acid,

the step which consists in introducing a for mate into a bath of sulfuric acid while maintaining throughout the mass a temperature below that at which substantial de' composition of formic acid occurs.

2. The method of making formic acid which consists in introducing a formate into a bath of sulfuric acid while maintaining throughout the mass a temperature below that at which substantial decomposition of formic acid occurs, and then heating the mass to distil formic acid.

3. In a method of making formic acid, the step which consists in introducing a formate into a bath of sulfuric acid, agitating the mixture, and cooling the same to maintain therein a temperature below that at which substantial decomposition of formic acid occurs. I

4. The method of making formic acid which consists in introducing a formate into a bath of sulfuric acid, agitating the mixture, cooling the same to maintain therein a temperature below that at which substantial decomposition of formic acid occurs, and then heating the mass to distil formic acid.

5. The method of making formic acid which consists in introducing a formate into a bath of sulfuric acid while maintaining throughout the mass a temperature below that at which substantial decomposition of formic acid occurs, and distilling formic acid under reduced pressure.

(3. The method of making formic acid which consists in introducing a formate into a bath of sulfuric acid, agitating the mixture, cooling the same to maintain therein a temperature below that at which substantial decomposition of formic acid occurs, and distilling formic acid therefrom under reduced pressure.

In testimony whereof, I aflix my signature in presence of two witnesses.

HENRY HOWARD.

Witnesses IDA MAY GRAHAM, WILLIAM FRANKLIN OBURG. 

